The present invention generally relates to a method of manufacturing lens caps for transistor outline packages adapted to package optoelectronic components, and particularly to a method of manufacturing ball lens caps for said transistor outline packages. The cross-referenced copending application with an unknown serial number filed on May 9, 2002, titled xe2x80x9cLENS CAP FOR TRANSISTOR OUTLINE PACKAGExe2x80x9d, discloses the article made from the method disclosed in this application.
Optoelectronic components, such as optical coupling devices, generally require a lens cap to protect them from damage and from EMI (Electro Magnetic Interference). Without such protection, damage can result from exposure to moisture, dirt, heat, radiation, or other hazards. The lens cap generally comprises a main part and a lens part. The lens part is usually coupled to the main part by a method including gluing, as disclosed in Japanese Application 2-165684. However, problems with this method include contamination of the lens part due to dispersion of the glue, which can affect the optical characteristics of the lens part. In addition, there is a danger that the lens part will become separated from the main part of the housing if the glue loses effectiveness over time. Furthermore, the method of manufacturing the lens cap is unduly costly and time-consuming.
Therefore, an improved method of manufacturing a lens cap for a transistor outline package that overcomes the above-mentioned disadvantages is desired.
A main object of the present invention is to provide a method of manufacturing a lens cap for a transistor outline package which produces a lens cap that holds up over time and whose optical characteristics are reliably good.
Another object of the present invention is to provide a method of manufacturing cheap lens caps for transistor outline packages in large quantity.
To achieve the above objects, a method of manufacturing lens caps for transistor outline packages is provided by the present invention. The manufactured lens cap comprises a lens part and a hollow main part adapted for receiving optoelectronic components. The lens part includes a ball lens having a first groove and a sprue filling portion having a second groove. The main part defines an opening which comprises a ball lens receiving hole communicating with a sprue. A sidestep is formed along an edge of the opening protruding into the sprue. Said method comprises: (a) providing the main part of the lens cap; (b) providing upper and lower molds and putting the main part into the molds; (c) closing the molds and insert molding the lens part. The ball lens has a diameter greater than the ball lens receiving hole. The lens part formed by this method is thus firmly coupled to the main part of the lens cap through the engagement of the protruding sidestep with the second groove and a circular rim of the main part with the first groove.